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Instance FB vs FC-DB cycle time

Created by: dendhondt at: 6/5/2013 4:21 PM (13 Replies)

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6/5/2013 4:21 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	Hi, I'm trying the make some standard blocks for s7 300 tia v11 Motor 1 direction, 2 direction, 2 speeds, freq-drive, valve digIn digOut AnalogIn AnalogOut i still doubt between Instanc fb and fc with global db i made for each block type an udt with always 32 bytes (some spares) Now i'm testing the differend posibilitys FC with input block number - in the begin and end of the block the data is loaded/ saved in the db using AR1/AR2 ( only the used bytes, not the spares) FC with 32bytes UDT as InOut Multi instanc FB also with 32 bytes to test Tested with 50 to 300 block calls Tested with IM151-8 PN CPU FC blocks generating a much higer cpu cyle time then the multi instance fb ?? the only thing i don't like with FB multi instance is when doing a change the DB has to be regenerated (All values to zero) why the big difference in cycle time? 50 FB calls +- 2 ms 50 FC Calls +- 15ms 240calls = 66 ms Attachment Standaard_UDT.pdf (434 Downloads)

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6/6/2013 2:35 AM	Rate (2)
fritz Diamond Member Joined: 10/7/2005 Last visit: 11/7/2024 Posts: 3026 Rating: (1057)	Hello dendhondt to start with, the executiontime for a Block is simply the sum of the execution time of all instructions that are in the Block. You can find out how long each instruction needs to execute in the SIMATIC S7-300 Instruction list S7-300 CPUs and ET 200 CPUs. Where it gets tricky to work this out is in the case of where you use a UDT as a Block Parameter (e.g. IN_OUT) and thenaccess the individual elementsof the UDT insidethe FC. If so, Step 7 creates a anwfull lot of"hidden" inddirect addressing related code to get the value of these UDT variables and you'll find out more about this in the thread Shall UDT make the difference in CPU Scan Time?. I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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6/6/2013 4:23 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	the document "memory requirments for word load commands"says: - direct access takes 2 bytes - FB multianstance 42 bytes - FC 48 bytes but i have a much bigger difference between fb-instance and fc 50 fc blocks udt as InOut 16 ms 50 FB instance 3 ms the fc with an udt as InOut looked like the best solution , very nice but the cycle time is too high because it would be at least 250 + the normal program the only way i got a better result is using blocknr as input and with pointer/AR1/AR first network load datafrom db to temp memory last network save data from temp memory to db then i get with 50 fc calls 7ms all tested with im151-8 pn cpu

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6/6/2013 5:47 PM	Rate (0)
AutoGen_405229 Experienced Member Joined: 2/18/2013 Last visit: 3/12/2024 Posts: 102 Rating: (23)	dendhondt but i have a much bigger difference between fb-instance and fc the only thing i don't like with FB multi instance is when doing a change the DB has to be regenerated (All values to zero) About the much bigger difference: The commands are quite different in complexity and of coursein runtime. There is no relation between number of Bytes and runtime! For details you should have a look into the instruction list. I would recommend going back to the FBsolution. About the FB solution: The DB doesn't haveto be downloaded in all changecases. As long as youdon'tchange the DB structure you don't have to download the DBaslong as you want avoid zeroing the values. And if you would change the DB structure you would have to download a global DB as well. If this doesn't make sense to you, maybeyoushould explain a little bit better which changes you would like to make without zeroing the values.

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6/6/2013 7:43 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	just changes like adding a block, deleting a block With FC you can just upload the DB Add A UDT at the end Transfer back to PLC Deleting -> Just rename to Spare The most proper solution is the FC DB With UDT as InOut Same flexibility as FB but not generating the DB DB with Motors M001 M002 M003 FC with Object declared InOut : Same UDT as in DB Object is then DB_Motors.M001 I also have a block with a blocknr as input and Load/save to DB using Pointer /AR1/AR2 With this the cycl time reduces to 7ms/50Calls I was trying to load/Save the InOut to Temp memory at beginning/end of the block And access to temp memory in programm So i ony load/save 2 times But i can't get it working like this

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6/7/2013 9:16 AM	Rate (0)
AutoGen_405229 Experienced Member Joined: 2/18/2013 Last visit: 3/12/2024 Posts: 102 Rating: (23)	dendhondt just changes like adding a block, deleting a block If that case you should work with individual instances instead of a multiinstance. I.e. create an FB Motor and then create one instance (DB) for each Motor. In this case you can add new Motor instances without affecting running Motor instancesinstances. Only if you make changes to the data structure of the Motor Instances (which are defined in the FB) running instances would be affected. But this would also happen if you use a FC and a global DB.

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6/7/2013 6:47 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	i'm still trying to find a proper solution, i'm not giving up i was trying to use a UBLOCKMOVE function then i need to make the adres only once not for each operation maybe this will reduce cycle time? INOUT #IO_Object Temp #Object first network copy #IO_Object to #Object Last network copy #Object to #IO_Object so i dit this L P#IO_Object LAR1 L P#Object LAR2 but this is not enough i need to make the any pointer source and detination adress

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6/8/2013 1:07 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	Hi, Does somebody have an idee how to copy udt from INOUT parameter to Temp parameter ?

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6/9/2013 4:00 PM	Rate (0)
dendhondt Bronze Member Joined: 8/5/2009 Last visit: 7/4/2022 Posts: 156 Rating: (7)	hi, i got it working using the UBLKMOV function I just have one question and i can't find it What is the difference between the BLKMOV and UBLKMOV function ? Do they copy the data in 1 cpu cycle or spread over more cycles if so, then my block is working fine, and cycle time is reduced to the same as fb instance call (tested wich 50 calls)
	Last edited by: dendhondt at: 6/9/2013 4:59 PM
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6/10/2013 8:24 AM	Rate (0)
AutoGen_405229 Experienced Member Joined: 2/18/2013 Last visit: 3/12/2024 Posts: 102 Rating: (23)	dendhondt I just have one question and i can't find it What is the difference between the BLKMOV and UBLKMOV function ? BLKMOV is interruptible and UBLKMOV is uninterruptible. Interruptible means, if other OBs or HMIs write tothe source data the data at the destination could be half old and half new.The same problemmay occurif they read from the destination data. On the other hand, non interruptible means that critical OBs with high priority may get delayeduntil a runningUBLKMOV is finished. Whether this is a problem or not depends on the amount of data you copy. And for that reason the UBLKMOV is limited to acertain max.amount of data, as far as Iremember to512 Bytes. So you need to trade off data consistencyagainst reaction times.

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